Mitosis
During mitosis, the cell divides into two daughter cells. Mitosis can be divided into four subphases: prophase, metaphase, anaphase, and telophase.
Prophase
Prophase begins when the double-chromatid chromosomes are fully formed and can be seen clearly under a microscope. After the chromosomes have formed, microtubule structures called centrioles move to opposite ends of the cell. As the centrioles separate, a fanlike array called the mitotic spindle forms between them. In later phases of mitosis, the spindle will function as a guide to help the replicated chromosomes divide neatly into two groups of complete genetic material.
In prophase, the nuclear membrane dissolves and the chromosomes attach to the spindle at their centromere. With chromosomes secured on the spindle, the cell is ready to enter the next phase of mitosis, metaphase.
Metaphase
Metaphase begins when the spindle is completely formed. The phase is marked by the alignment of chromosomes at the middle of the cell, halfway between each of the mitotic spindle poles along a plane called the metaphase plate.
Once the chromosomes are aligned correctly, the cell enters anaphase, the third stage of mitosis.
Anaphase
During anaphase, the pairs of chromosomes at the center of the cell separate into individual chromosomes, which move to opposite sides of the cell. The microtubule and spindle fibers facilitate this motion. The cell also begins to elongate in preparation for splitting.
When the chromosomes reach their destination at the opposite poles of the cell, anaphase gives way to telophase, the fourth and final stage of mitosis.
Telophase
Telophase begins when the chromosomes reach opposite poles. Small pieces of nuclear membrane in the cell begin to re-form around the group of chromosomes at each end, creating two nuclei in one cell. When the chromosomes are once again surrounded by a protective envelope, they relax and resume their interphase appearance as a stringy tangle. No longer needed, the spindles fall apart during this stage, and a nucleolus re-forms inside each nucleus.
Cytokinesis
Although mitosis officially ends with telophase, at this point, the cell is not yet actually split into two new cells. The final cleavage is not exactly its own stage, but it does have its own name: cytokinesis, literally “cell division.”
When the two nuclei reach opposite poles of the cell, the cell in the middle, ultimately leading to cleavage.
